This invention relates to a semiconductor device in which the circuit composed on a semiconductor substrate is operated when either one or both of a supply potential and grounding potential are supplied from outside the semiconductor substrate.
Recently, as semiconductor devices are becoming higher in their degree of integration and faster in operation, miniaturization of patterns and multiple-layer wiring structures on the semiconductor substrate are being promoted.
FIG. 9 shows a conventional example of a method of supplying a supply potential and a grounding potential in a semiconductor device.
A semiconductor substrate 1 comprises, on its upper surface, a wire bonding pad (Vcc pad) 2 for feeding a supply potential (called Vcc) from outside the semiconductor substrate 1, and a wire bonding pad (Vss pad) 3 for supplying a grounding potential (called Vss) from outside the semiconductor substrate 1. An entire circuit 4 is composed on the semiconductor substrate 1, and the pads 2 and 3 are connected respectively by means of Vcc wiring 5 and Vss wiring 6. The Vcc pad 2 is provided with Vcc from an external lead for Vcc 7 through a Vcc feed wire 8, and the Vss pad 3 is provided with Vss from an external lead for Vss 9 through a Vss feed wire 10.
In this constitution, the entire circuit 4 composed on the semiconductor substrate 1 is operated when provided with Vcc through common Vcc feed part (7, 8, 2, 5), and with Vss through common Vss feed part (9, 10, 3, 6).
Generally, the Vcc feed part (7, 8, 2, 5) and Vss feed part (9, 10, 3, 6) are made of metals having an extermely small resistance. Recently, however, as a result of fine-pattern and multiple-layer structure in the trend of a higher degree of integration of semiconductor devices, the wiring layer has become extremely thin, and the resistance ignored hitherto can no longer be disregarded, which has induced various problems.
For example, if there is an output transistor for transmitting signals to outside of the semiconductor device 1 in the entire circuit 4, the current flowing in this output transistor is much larger than the current flowing in the other circuits.
Fluctuations of Vcc and Vss during operation of the output transistor are shown in FIG. 10.
When the output transistor operates, a current flows into the output transistor from the external lead for Vcc 7 shown in FIG. 9 through wire 8, pad 2 and wiring 5, and from the output transistor the current flows into the external lead for Vss 9 through wiring 6, pad 3, and wire 10. At this time, the unignorable resistance is present in the Vcc feed part and Vss feed part as mentioned above, and this resistance causes the production of a potential difference between the Vcc outside the semiconductor substrate 1 and the Vcc supplied in the internal cirucit. Similarly, a potential difference occurs between the Vss outside the semiconductor substrate 1 and the Vss supplied in the internal circuit. As a result of these potential differences, the internal circuits other than the output transistor malfunction.
FIG. 11 shows changes of the output signal potential from the output transistor when other internal circuits operate during operation of the output transistor.
During operation of the output transistor, if other internal circuits operate, a current flows into the Vcc feed part and Vss feed part by the operation of the internal circuits, and changes occur in the Vcc and Vss to be supplied in the output transistor, so that a distortion is caused in the output signal potential of the output transistor.